Antibiotic Prophylaxis to Prevent Obesity-Related Induction Complications in Nulliparae at Term: a pilot randomized controlled trial.

BACKGROUND: Women with obesity are at increased risk of complications during and after labor and delivery, including puerperal infection and cesarean delivery. As labor induction has become increasingly common, it is crucial to find ways to decrease complication rates in this high-risk population. OBJECTIVE: This study aimed to explore the effect of prophylactic antibiotics during labor induction of nulliparous women with obesity on the rates of cesarean delivery and puerperal infection and to estimate the parameters needed to calculate the sample size for a larger, multicenter trial. STUDY DESIGN: In this randomized, placebo-controlled pilot trial, nulliparous patients with a body mass index of ≥30 kg/m2 were randomized to either prophylactic antibiotics (500 mg azithromycin for 1 dose and 2 g cefazolin every 8 hours for up to 3 doses) or placebo, administered starting at the beginning of labor induction. The exclusion criteria were known fetal anomaly, fetal demise, multifetal gestation, ruptured membranes >12 hours, infection requiring antibiotics at the start of labor induction, and/or allergy to azithromycin or beta-lactam antibiotics. The co-primary outcomes were rates of puerperal infection (composite of chorioamnionitis, endometritis, and/or cesarean delivery wound infection) and cesarean delivery. Participants were followed up for 30 days after delivery, and maternal and neonatal demographic and outcome data were collected. Proportions and 95% confidence limits were calculated for each of these outcomes. RESULTS: From January 2019 to May 2021, 101 patients were randomized in the class III stratum (1 patient who was randomized ultimately did not undergo labor induction). From February 2020 to May 2021, 38 and 47 patients were randomized to class I and II strata, respectively (to assess the effect of obesity class on the outcomes expected to be influenced by antibiotic prophylaxis). In the antibiotics and placebo groups, the rates of cesarean delivery were 29.0% (95% confidence interval, 19.8-38.3) and 39.8% (95% confidence interval, 29.8-49.7), respectively, and puerperal infection occurred in 8.6% (95% confidence interval, 2.9-14.3) and 9.7% (95% confidence interval, 3.7-15.7), respectively. In the subgroup with class III obesity, in the antibiotics and placebo groups, the rates of cesarean delivery were 33.3% (95% confidence interval, 20.4-47.9) and 46.0% (95% confidence interval, 32.2-59.8), respectively, and puerperal infection occurred in 7.8% (95% confidence interval, 0.5-15.2) and 10.0% (95% confidence interval, 1.7-18.3), respectively. Note that this pilot study was not powered to detect differences of this magnitude but rather to estimate parameters. CONCLUSION: The administration of prophylactic antibiotics during labor induction of nulliparous patients with obesity resulted in a 27% lower cesarean delivery rate overall and a 28% lower rate in patients with class III obesity. A larger trial is warranted to evaluate these differences.

Clinical effectiveness of adding azithromycin to antimicrobial prophylaxis for cesarean delivery.

BACKGROUND: A recent large clinical trial demonstrated an approximately 50% decrease in the rate of postoperative infection in women who were laboring and/or had rupture of membranes for >4 hours and who received azithromycin in addition to standard preoperative antibiotic prophylaxis at the time of cesarean delivery. Given these results, our institution made a policy change in May 2017 to add azithromycin to standard preoperative prophylaxis for all cesarean deliveries. OBJECTIVE: This study aimed to evaluate the clinical effectiveness of adding azithromycin to preoperative antibiotic prophylaxis for cesarean delivery. STUDY DESIGN: We conducted a before-and-after cohort study of women delivered via cesarean delivery at our institution. The preimplementation group included women who delivered from March 1, 2016, to February 28, 2017, (before an institutional practice change of adding azithromycin to standard preoperative prophylaxis), and the postimplementation group included women who delivered from September 1, 2017, to August 31, 2018 (allowing a 6-month period for uptake of the practice change). The primary outcome was a composite of postoperative infections (endometritis, wound infection, other maternal infections). Unadjusted and adjusted risk ratios and 95% confidence intervals were estimated using a modified Poisson regression model. RESULTS: In the preimplementation (n=1171) and postimplementation (n=1168) groups, the incidence rates of the composite outcomes were 4.7% and 5.3%, respectively (P=.49). Both unadjusted (relative risk, 1.13; 95% confidence interval, 0.78-1.62) and adjusted (adjusted relative risk, 1.06; 95% confidence interval, 0.74-1.52) comparisons were not significantly different. In addition, results were statistically nonsignificant, but in the direction of lower rates of infection, in the after cohort for women in labor and/or with rupture of membranes for ≥4 hours (relative risk, 0.88 [95% confidence interval, 0.56-1.39]; adjusted relative risk, 0.82 [95% confidence interval, 0.52-1.30]) and for women with clinical chorioamnionitis (relative risk, 0.37 [95% confidence interval, 0.08-1.67]; data too sparse for adjusted analysis). In the subgroup of women who were not in labor, the after cohort had a statistically nonsignificant increased risk of the composite outcome in both unadjusted (relative risk, 1.53; 95% confidence interval, 0.86-2.72) and adjusted (adjusted relative risk, 1.48; 95% confidence interval, 0.83-2.65]) comparisons. CONCLUSION: In clinical practice, the addition of azithromycin to standard preoperative antibiotic prophylaxis for cesarean delivery may have an effect size smaller than seen in the large clinical trial prompting this practice change. Extrapolation of this regimen to women not in labor may be ineffective.

Prenatal diagnosis of middle interhemispheric variant of holoprosencephaly: Report of two cases.

Holoprosencephaly ranges in severity based on the degree of anatomic abnormality. Middle interhemispheric variant of holoprosencephaly is a less common and often milder variant that has the characteristic sonographic findings of an absent cavum septum pellucidum and a single fused ventricle. This subtype may be associated with genetic conditions that have not been well-described in the literature. We present two cases of middle interhemispheric variant of holoprosencephaly diagnosed on fetal ultrasound.

Maternal Mortality Among American Indian/Alaska Native Women: A Scoping Review.

Background: Maternal mortality decreased globally by about 38% between 2000 and 2017, yet, it continues to climb in the United States. Gaping disparities exist in U.S. maternal mortality between white (referent group) and minority women. Despite important and appropriate attention to disparities for black women, almost no attention has been given to American Indian/Alaska Native (AI/AN) women. The purpose of this scoping review is to synthesize available literature concerning AI/AN maternal mortality. Methods: Databases were searched using the terms maternal mortality and pregnancy-related death, each paired with American Indian, Native American, Alaska Native, Inuit, and Indigenous. Criteria (e.g., hemorrhage) were paired with initial search terms. Next, pregnancy-associated death was paired with American Indian, Native American, Alaska Native, Inuit, and Indigenous. Criteria in this category were homicide, suicide, and substance use. Results: The three leading causes of AI/AN pregnancy-related maternal mortality are hemorrhage, cardiomyopathies, and hypertensive disorders of pregnancy. AI/AN maternal mortality data for homicide and suicide consistently include small samples and often categorize AI/AN maternal deaths in an "Other" race/ethnicity, which precludes targeted AI/AN data analysis. No studies that reported AI/AN maternal mortality as a result of substance use were found. Health care characteristics such as quality, access, and location also may influence maternal outcomes and maternal mortality. Conclusions: Despite AI/AN maternal mortality being disproportionately high compared to other racial/ethnic groups, relatively little is known about root causes.

Insulin Dosing, Glycemic Control, and Perinatal Outcomes in Pregnancies Complicated by Type-2 Diabetes.

OBJECTIVE: This study aimed to evaluate the prevalence of severe insulin resistance (insulin requirements ≥2 units/kg) at delivery and the relationship between severe insulin resistance, glycemic control, and adverse perinatal outcomes in pregnant women with type-2 diabetes mellitus. STUDY DESIGN: This is a retrospective cohort study of women with type-2 diabetes mellitus who delivered between January 2015 and December 2017 at a tertiary academic medical center. Maternal demographic information, self-monitored blood sugars, and insulin doses were abstracted from the medical record. Multivariable logistic regression was used to identify maternal baseline characteristics associated with severe insulin resistance at delivery. RESULTS: Overall 72/160 (45%) of women had severe insulin resistance. Women in the severe insulin resistance group demonstrated evidence of suboptimal glycemic control as evidenced by higher mean hemoglobin A1c (HbA1c) values (7.2 [ ± 1.1] vs. 6.6 [ ± 1.3%], p = 0.003), higher mean fasting (104.0 [ ± 17.4] vs. 95.2 [ ± 11.7 mg/dL], p < 0.001) and postprandial glucose values (132.4 [ ± 17.2] vs. 121.9 [ ± 16.9 mg/dL]), p < 0.001), and a higher percentage of total glucose values that were elevated above targets (37.7 [95% confidence interval (CI): 26.8-50] vs. 25.6 [95% CI: 13.3-41.3%], p < 0.001). Maternal HbA1c ≥6.5% and insulin use prior to pregnancy were associated with a higher prevalence of severe insulin resistance, while Hispanic ethnicity and non-White race were associated with a lower prevalence of severe insulin resistance. The rates of adverse perinatal outcomes including large for gestational age (LGA) birth weight, cesarean delivery, and hypertensive disorders of pregnancy did not differ between groups. CONCLUSION: Severe insulin resistance is common among pregnant women with type-2 diabetes, and it is associated with suboptimal glycemic control. Future studies are necessary to develop strategies to identify women with severe insulin resistance early in pregnancy and facilitate adequate insulin dosing. KEY POINTS: · Severe insulin resistance is common.. · BMI does not predict severe insulin resistance.. · Suboptimal glycemic control is common..

Impact of a Policy to Deliver at 39 Weeks for the Indication of Class III Obesity.

OBJECTIVE: The aim of this study was to evaluate the effect of a policy to deliver at 39 weeks for class III obesity. METHODS: This was a retrospective cohort study of women with class III obesity delivering at ≥ 37 weeks before (May 2012 to April 2014) and after the policy (September 2014 to August 2016). The primary outcome was the cesarean rate. Secondary outcomes included maternal morbidities and a neonatal morbidity composite. Modified Poisson regression was used to adjust for demographic differences between groups. RESULTS: The study included a total of 1,210 patients, 580 before the policy and 630 after the policy. Before and after the policy, cesarean rates were similar (41.6% vs. 47.1%; risk ratio [RR]: 1.13 [95% CI: 1.00-1.29]; adjusted RR [aRR]: 1.03 [95% CI: 0.92-1.14]). In adjusted comparisons of women undergoing labor induction, parous women had lower cesarean rates (aRR: 0.62; 95% CI: 0.41-0.94) but nulliparous women had higher cesarean rates (aRR: 1.32; 95% CI: 1.04-1.68) after the policy (P for interaction = 0.01). Rates of chorioamnionitis, endometritis, and cesarean wound infection were not different between groups. Composite neonatal morbidity was not different between pre- and postpolicy groups. CONCLUSIONS: A policy of delivery at 39 weeks for class III obesity did not affect overall cesarean rate or rates of maternal or neonatal morbidity. Further investigation should evaluate subsets of women who may have a higher cesarean rate with this policy.

A Case of Maternal Sepsis and Fetal Demise Associated with Streptococcus pseudoporcinus.

Streptococcus pseudoporcinus has recently been described in relation to its colonization of the female genitourinary tract. Since prior reports have linked S. pseudoporcinus only with minor morbidities, the organism previously has not been considered to be a cause of serious puerperal infections. A 41-year-old gravida 2, para 1-0-0-1 presented with abdominal pain and intrauterine fetal demise. A beta hemolytic Streptococcus was isolated from her placenta, endometrium, urine, and two blood culture sets. The isolate was a Streptococcus pseudoporcinus, which colonizes the female genital tract and can resemble Streptococcus agalactiae. This case demonstrates that S. pseudoporcinus is a potential cause of severe maternal and fetal morbidity and mortality.

Genetic loss of proadrenomedullin N-terminal 20 peptide (PAMP) in mice is compatible with survival.

Adrenomedullin (AM) and proadrenomedullin N-terminal 20 peptide (PAMP) are small peptides derived from a common precursor, pre-proadrenomedullin. Although AM and PAMP share hypotensive effects in the cardiovascular system, the peptides also exert diverse and distinct effects on endocrine physiology, innate immunity, cytoskeletal biology and receptor signaling pathways. Tremendous knowledge has been gleaned from the study of several genetic animal models of AM deletion or overexpression, some of which also simultaneously delete the coding region for PAMP peptide. However, deletion of PAMP without concurrent deletion of AM in an animal model is not currently available for the study of PAMP function. Here, we present the generation of AdmΔPAMP/ΔPAMP and AdmΔPAMP/- mice, which lack the coding sequence for PAMP while preserving the coding sequence for AM. AdmΔPAMP/ΔPAMP mice survive to adulthood without any obvious abnormalities and are fertile, though AdmΔPAMP/- females have small litters. Interestingly, these animals express lower levels of Adm mRNA and AM peptide than wild type animals, but these levels are still compatible with survival. Importantly, despite reduced levels, the spatiotemporal expression of AM peptide within the hearts of AdmΔPAMP/- mice remains similar to wild type animals. AdmΔPAMP/ΔPAMP mice are now a publicly available tool for future investigations of PAMP function.

Adrenomedullin improves fertility and promotes pinopodes and cell junctions in the peri-implantation endometrium.

Implantation is a complex event demanding contributions from both embryo and endometrium. Despite advances in assisted reproduction, endometrial receptivity defects persist as a barrier to successful implantation in women with infertility. We previously demonstrated that maternal haploinsufficiency for the endocrine peptide adrenomedullin (AM) in mice confers a subfertility phenotype characterized by defective uterine receptivity and sparse epithelial pinopode coverage. The strong link between AM and implantation suggested the compelling hypothesis that administration of AM prior to implantation may improve fertility, protect against pregnancy complications, and ultimately lead to better maternal and fetal outcomes. Here, we demonstrate that intrauterine delivery of AM prior to blastocyst transfer improves the embryo implantation rate and spacing within the uterus. We then use genetic decrease-of-function and pharmacologic gain-of-function mouse models to identify potential mechanisms by which AM confers enhanced implantation success. In epithelium, we find that AM accelerates the kinetics of pinopode formation and water transport and that, in stroma, AM promotes connexin 43 expression, gap junction communication, and barrier integrity of the primary decidual zone. Ultimately, our findings advance our understanding of the contributions of AM to uterine receptivity and suggest potential broad use for AM as therapy to encourage healthy embryo implantation, for example, in combination with in vitro fertilization.

Enhanced Uterine Contractility and Stillbirth in Mice Lacking G Protein-Coupled Receptor Kinase 6 (GRK6): Implications for Oxytocin Receptor Desensitization.

Oxytocin is a potent uterotonic agent and is used clinically for induction and augmentation of labor, as well as for prevention and treatment of postpartum hemorrhage. Oxytocin increases uterine contractility by activating the oxytocin receptor (OXTR), a member of the G protein-coupled receptor family, which is prone to molecular desensitization. After oxytocin binding, the OXTR is phosphorylated by a member of the G protein-coupled receptor kinase (GRK) family, which allows for recruitment of ß-arrestin, receptor internalization, and desensitization. According to previous in vitro analyses, desensitization of calcium signaling by the OXTR is mediated by GRK6. The objective of this study was to determine the role of GRK6 in mediating uterine contractility. Here, we demonstrate that uterine GRK6 levels increase in pregnancy and using a telemetry device to measure changes in uterine contractility in live mice during labor, show that mice lacking GRK6 produce a phenotype of enhanced uterine contractility during both spontaneous and oxytocin-induced labor compared with wild-type or GRK5 knockout mice. In addition, the observed enhanced contractility was associated with high rates of term stillbirth. Lastly, using a heterologous in vitro model, we show that ß-arrestin recruitment to the OXTR, which is necessary for homologous OXTR desensitization, is dependent on GRK6. Our findings suggest that GRK6-mediated OXTR desensitization in labor is necessary for normal uterine contractile patterns and optimal fetal outcome.

Intrauterine telemetry to measure mouse contractile pressure in vivo.

A complex integration of molecular and electrical signals is needed to transform a quiescent uterus into a contractile organ at the end of pregnancy. Despite the discovery of key regulators of uterine contractility, this process is still not fully understood. Transgenic mice provide an ideal model in which to study parturition. Previously, the only method to study uterine contractility in the mouse was ex vivo isometric tension recordings, which are suboptimal for several reasons. The uterus must be removed from its physiological environment, a limited time course of investigation is possible, and the mice must be sacrificed. The recent development of radiometric telemetry has allowed for longitudinal, real-time measurements of in vivo intrauterine pressure in mice. Here, the implantation of an intrauterine telemeter to measure pressure changes in the mouse uterus from mid-pregnancy until delivery is described. By comparing differences in pressures between wild type and transgenic mice, the physiological impact of a gene of interest can be elucidated. This technique should expedite the development of therapeutics used to treat myometrial disorders during pregnancy, including preterm labor.

Overexpression of the SK3 channel alters vascular remodeling during pregnancy, leading to fetal demise.

The maternal cardiovascular system undergoes hemodynamic changes during pregnancy via angiogenesis and vasodilation to ensure adequate perfusion of the placenta. Improper vascularization at the maternal-fetal interface can cause pregnancy complications and poor fetal outcomes. Recent evidence indicates that small conductance Ca(2+)-activated K(+) channel subtype 3 (SK3) contributes to vascular remodeling during pregnancy, and we hypothesized that abnormal SK3 channel expression would alter the ability of the maternal cardiovascular system to adapt to pregnancy demands and lead to poor fetal outcomes. We investigated this hypothesis using transgenic Kcnn3(tm1Jpad)/Kcnn3(tm1Jpad) (SK3(T/T)) mice that overexpress the channel. Isolated pressurized uterine arteries from nonpregnant transgenic SK3(T/T) mice had larger basal diameters and decreased agonist-induced constriction than those from their wild-type counterparts; however, non-receptor-mediated depolarization remained intact. In addition to vascular changes, heart rates and ejection fraction were increased, whereas end systolic volume was reduced in SK3(T/T) mice compared with their wild-type littermates. Uterine sonography of the fetuses on pregnancy day 14 showed a significant decrease in fetal size in SK3(T/T) compared with wild-type mice; thus, SK3(T/T) mice displayed an intrauterine growth-restricted phenotype. The SK3(T/T) mice showed decreased placental thicknesses and higher incidence of fetal loss, losing over half of their complement of pups by midgestation. These results establish that the SK3 channel contributes to both maternal and fetal outcomes during pregnancy and point to the importance of SK3 channel regulation in maintaining a healthy pregnancy.

Altered contribution of RhoA/Rho kinase signaling in contractile activity of myometrium in leptin receptor-deficient mice.

In late gestation, enhanced myometrial contractility is mediated in part through increased Rho/Rho kinase. Since leptin, which is elevated in pregnancy and obesity, can directly depress myometrial function, we hypothesized that in leptin receptor-deficient mice, myometrial contractility would be greater in late pregnancy due to increased Rho/Rho kinase activity. To test this, we correlated RhoA and Rho kinase expression to contractility in myometrium from nonpregnant (NP) and late-pregnant (P18) heterozygous leptin receptor-deficient mice (db/+) vs. wild-type (WT) mice. In NP mice, KCl-induced contractions were similar between WT and db/+ myometrium. However, the Rho kinase-dependent component of the contractions was greater in db/+ mice, along with an increased expression of Rho kinase. KCl-induced contractions increased in strength in myometrium from P18 WT and db/+ compared with NP. Although the contribution of Rho kinase to contractions was unchanged in P18 WT mice, it was decreased in P18 db/+ mice. The decrease in Rho kinase-dependent contractions in P18 db/+ mice coincided with reduced RhoA and Rho kinase expression relative to NP db/+. Addition of high-fat-induced abnormal glucose utilization prevented changes in Rho kinase function. We conclude that abnormal leptin signaling increases expression and function of Rho kinase to maintain contractile function in NP myometrium and that during pregnancy the contribution of RhoA and Rho kinase expression to myometrial function is reduced despite an increase in myometrial contractility. Thus, other signaling mechanisms appear to compensate when leptin signaling is reduced to maintain contractile function during pregnancy.

The contribution of Kv7 channels to pregnant mouse and human myometrial contractility.

Premature birth accounts for approximately 75% of neonatal mortality and morbidity in the developed world. Despite this, methods for identifying and treating women at risk of preterm labour are limited and many women still present in preterm labour requiring tocolytic therapy to suppress uterine contractility. The aim of this study was to assess the utility of Kv7 channel activators as potential uterine smooth muscle (myometrium) relaxants in tissues from pregnant mice and women. Myometrium was obtained from early and late pregnant mice and from lipopolysaccharide (LPS)-injected mice (day 15 of gestation; model of infection in pregnancy). Human myometrium was obtained at the time of Caesarean section from women at term (38-41 weeks). RT-PCR/qRT-PCR detected KCNQ and KCNE expression in mouse and human myometrium. In mice, there was a global suppression of all KCNQ isoforms, except KCNQ3, in early pregnancy (n= 6, P < 0.001 versus late pregnant); expression subsequently increased in late pregnancy (n= 6). KCNE isoforms were also gestationally regulated (P < 0.05). KCNQ and KCNE isoform expression was slightly down-regulated in myometrium from LPS-treated-mice versus controls (P < 0.05, n= 3-4). XE991 (10 µM, Kv7 inhibitor) significantly increased spontaneous myometrial contractions in vitro in both human and mouse myometrial tissues (P < 0.05) and retigabine/flupirtine (20 µM, Kv7 channel activators) caused profound myometrial relaxation (P < 0.05). In summary, Kv7 activators suppressed myometrial contraction and KCNQ gene expression was sustained throughout gestation, particularly at term. Consequently, activation of the encoded channels represents a novel mechanism for treatment of preterm labour.

SK3 channel expression during pregnancy is regulated through estrogen and Sp factor-mediated transcriptional control of the KCNN3 gene.

Overexpression of the small-conductance calcium-activated K(+) channel 3 (SK3) in transgenic mice compromises parturition, suggesting that the SK3 channel plays a role in pregnancy. In wild-type mouse myometrium, expression of SK3 transcript and protein is significantly reduced during pregnancy, but the mechanism(s) responsible for this attenuation of channel expression is unknown. The promoter region of the SK3-encoding mouse KCNN3 gene contains two binding sites for specificity protein (Sp) transcription factors, two of which are expressed in the uterus: Sp1, which enhances gene transcription in response to estrogen; and Sp3, which competes for the same binding motif as Sp1 and can repress gene expression. We investigated the hypothesis that Sp1 and Sp3 regulate SK3 channel expression during pregnancy. In mouse myometrium, Sp1 expression was reduced during late gestation, whereas Sp3 expression levels were constant throughout pregnancy. Using a reporter system, we found that Sp1 overexpression resulted in a significant increase in SK3 promoter activation and that Sp3 cotransfection reduced promoter activation to basal levels. These findings indicate that Sp3 outcompetes Sp1 to decrease SK3 transcription. To determine whether high levels of estrogen in vivo can affect the regulation of SK3 protein levels by Sp factors, ovariectomized mice were implanted with a 17ß-estradiol or placebo pellet for 3 wk; estrogen-treated mice had reduced uterine SK3 protein expression compared with placebo-treated counterparts. In human myometrial cells overexpressing Sp1, estrogen treatment stimulated expression of the SK3 transcript. Overall, our findings indicate that Sp1 and Sp3 compete to regulate SK3 channel expression during pregnancy in response to stimulation by estrogen.

In vivo measurement of intrauterine pressure by telemetry: a new approach for studying parturition in mouse models.

Transgenic and knockout mouse models have proven useful in the study of genes necessary for parturition-including genes that affect the timing and/or progression of labor contractions. However, taking full advantage of these models will require a detailed characterization of the contractile patterns in the mouse uterus. Currently the best methodology for this has been measurement of isometric tension in isolated muscle strips in vitro. However, this methodology does not provide a real-time measure of changes in uterine pressure over the course of pregnancy. Recent advances have opened the possibility of using radiotelemetric devices to more accurately and comprehensively study intrauterine pressure in vivo. We tested the effectiveness of this technology in the mouse, in both wild-type (WT) mice and a mouse model of defective parturition (SK3 channel-overexpressing mice), after surgical implant of telemetry transmitters into the uterine horn. Continuous recordings from day 18 of pregnancy through delivery revealed that WT mice typically deliver during the 12-h dark cycle after 19.5 days postcoitum. In these mice, intrauterine pressure gradually increases during this cycle, to threefold greater than that measured during the 12-h cycle before delivery. SK3-overexpressing mice, by contrast, exhibited lower intrauterine pressure over the same period. These results are consistent with the outcome of previous in vitro studies, and they indicate that telemetry is an accurate method for measuring uterine contraction, and hence parturition, in mice. The use of this technology will lead to important novel insights into changes in intrauterine pressure during the course of pregnancy.

Overexpression of SK3 channels dampens uterine contractility to prevent preterm labor in mice.

The mechanisms that control the timing of labor have yet to be fully characterized. In a previous study, the overexpression of small conductance calcium-activated K(+) channel isoform 3 in transgenic mice, Kcnn3(tm1Jpad)/Kcnn3(tm1Jpad) (also known as SK3(T/T)), led to compromised parturition, which indicates that KCNN3 (also known as SK3) plays an important role in the delivery process. Based on these findings, we hypothesized that SK3 channel expression must be downregulated late in pregnancy to enable the uterus to produce the forceful contractions required for parturition. Thus, we investigated the effects of SK3 channel expression on gestation and parturition, comparing SK3(T/T) mice to wild type (WT) mice. Here, we show in WT mice that SK3 transcript and protein are significantly reduced during pregnancy. We also found the force produced by uterine strips from Pregnancy Day 19 (P19) SK3(T/T) mice was significantly less than that measured in WT or SK3 knockout control (SK3(DOX)) uterine strips, and this effect was reversed by application of the SK3 channel inhibitor apamin. Moreover, two treatments that induce labor in mice failed to result in complete delivery in SK3(T/T) mice within 48 h after injection. Thus, stimuli that initiate parturition under normal circumstances are insufficient to coordinate the uterine contractions needed for the completion of delivery when SK3 channel activity is in excess. Our data indicate that SK3 channels must be downregulated for the gravid uterus to generate labor contractions sufficient for delivery in both term and preterm mice.